The present invention relates to collimator gun sights. With such collimator sights, light from a suitably illuminated graticule pattern or other aiming mark is collimated for presentation to an eye of the user of the weapon as an image of the aiming mark at infinity, or at a predetermined distance where appropriate. In one arrangement, the other eye of the user is free to view the target so that, when the brightness levels of the aiming mark and the target are correctly balanced, the user will perceive the aiming point superimposed on the viewed target. It is also known to provide various arrangements for presenting both the collimated light from the image of the aiming point and light from the target to one or both eyes of the user simultaneously. A simple arrangement for doing this which is known is to provide a partially reflecting concave mirror suitably placed to reflect back to the aiming eye of the user of the weapon light from means defining the graticule pattern. If the distance between the concave mirror and the graticule pattern corresponds to the focal length of the concave mirror, the image seen in the concave mirror will appear to be substantially at infinity. The user of the weapon can then view the target field through the partially reflecting mirror whilst simultaneously seeing the image of the graticule pattern at infinity in the mirror. It is usual to ensure that the partially reflecting mirror provides substantially no deflection to light passing through the mirror from the target field so as to minimise any distortion of the target as seen by the user. Thus, it is known to employ a parallel faced meniscus glass for the partially reflecting mirror with one surface of the meniscus glass suitably coated to provide the reflecting surface.
It is also known to form a collimator sight as a block or rod of optically transparent material with the partially reflecting mirror formed at one end of the rod. The means defining the graticule pattern is embedded in the rod so that the light path from the graticule pattern to the partially reflecting surface is entirely within the material of the rod. An example of this type of sight is disclosed in U.S. Pat. No. 3,942,901.